CompressKit - Image Compressor
CompressKit makes photos smaller so they are quicker to email, upload and store. Select up to ten JPEG or PNG images, choose one of three compression levels and the app re-encodes them as JPEG files, showing the size before and after and how much space you saved.
It is meant for everyday jobs: a web form that rejects attachments over a few megabytes, a batch of holiday pictures for a family chat, product photos for a listing, or screenshots that need to fit in an email. Large images are scaled down so that the shorter side is 1080 pixels, which is plenty for phones, social media and most web pages.
In the browser everything happens on your own device. The pictures are not uploaded to a server, and nothing is kept after you close the page.
The app runs entirely in your browser. What you enter is saved only on this device.
How to use CompressKit
- Select your images. Tap Select Images and choose up to ten JPEG or PNG files. The next screen shows thumbnails with each file's name and size, plus the total size.
- Adjust the selection. Tap the red cross on a thumbnail to remove it, or use Add More to pick further images, as long as the total stays at ten or fewer.
- Choose a compression level. High Quality uses JPEG quality 90, Balanced uses 70 and Small Size uses 50. Lower quality means smaller files but more visible artefacts.
- Compress. Tap Compress Images. A progress screen shows each image as waiting, compressing or completed. You can cancel while it runs.
- Check the result. The summary shows the original size, the compressed size and the amount saved as a size and a percentage, followed by each compressed image.
- Save or share. Tap Save to download the compressed files (named like photo_compressed.jpg) or Share to send them through your browser's share sheet where supported. Compress More Images starts again.
Features
- Batch compression of up to 10 images at a time
- Accepts JPEG and PNG and outputs JPEG
- Three levels: High Quality (90), Balanced (70), Small Size (50)
- Large images scaled so the shorter side is 1080 px; small images are never enlarged
- Before and after sizes with the percentage saved
- Per-image progress with a cancel option
- Download or share the compressed files
- Processing happens locally in your browser
- Interface in many languages
How image compression works
Why photos are so large
A modern phone camera captures 12 to 50 megapixels, and each photo is usually saved at high quality to keep every detail. That is useful for printing or cropping, but a 4,000-pixel-wide picture shown on a 400-pixel phone screen or in a chat thread carries far more data than anyone will see. Reducing both the pixel dimensions and the encoding quality removes most of that excess.
JPEG quality settings
JPEG is a lossy format: it divides the image into small blocks and stores fine detail more coarsely, with the quality number controlling how much is discarded. Around 90 the difference from the original is hard to spot. Around 70, which is a common default on the web, files shrink a lot and most photos still look clean. Around 50, smooth gradients such as skies can show banding and sharp edges can pick up faint halos, but the file becomes very small.
Because each save throws information away, compress from the original rather than re-compressing an already compressed copy over and over.
Resolution matters as much as quality
File size grows roughly with the number of pixels, so halving the width and height cuts the data to about a quarter before quality is even considered. A shorter side of 1080 pixels matches the width many social networks display and is sharp on most phone screens. If you need a large print or plan to crop heavily later, keep the original as well.
PNG versus JPEG
PNG is lossless and is ideal for screenshots, logos and graphics with flat colours or text, but it is inefficient for photographs. Converting a photo from PNG to JPEG often saves a great deal of space. Two things to keep in mind: JPEG has no transparency, so transparent areas become white, and very sharp text or line art can look slightly softer after conversion.
Choosing a level
Use High Quality for photos you care about or may edit later, Balanced for sharing and web uploads, and Small Size when a strict size limit matters more than detail. If a result looks too soft, run the original again at a higher level.
Frequently asked questions
Are my photos uploaded anywhere?
No. Images are read and compressed inside your browser on your device. Nothing is sent to a server and no account is needed.
Is anything saved after I leave?
No. Selected images and the recent compressions list live only in memory while the page is open, so reloading or closing the tab clears them. Download the files you want to keep.
Why did my PNG become a JPEG?
CompressKit always writes JPEG because it produces much smaller files for photos. Transparent areas are filled with white.
Will a small image get bigger?
Images are never enlarged. If an image is already small and heavily compressed, the result may save little, and a low-resolution PNG may not shrink much either.
Why can I only pick ten images?
The limit keeps batches quick and memory use reasonable. Run several batches for larger sets.
Does it keep photo metadata?
The compressed file is a fresh JPEG drawn from the decoded image, so location and camera details from the original are not copied over.
What is different from the phone app?
The iPhone and Android apps save the compressed images straight to your photo library. On the web the files are downloaded instead, and sharing depends on your browser's support for sharing files.
Limitations of the web version
- Compressed images are downloaded rather than saved to a photo library
- Sharing files works only in browsers that support the Web Share API with files
- Output is always JPEG; transparency is not kept
- Nothing is kept after the page is reloaded or closed
- Very large images may be slow on older devices because processing runs locally
Phone app
CompressKit is also available as an app for phones and tablets: